Accuracy evaluation of orthodontic movements with aligners: a prospective observational study

BACKGROUND: Since their introduction in orthodontics, clear aligners have been appreciated by patients, including adults, for their comfort and low aesthetic impact. Despite the enormous mobilization of financial resources all over the world aimed at producing new product lines, few clinical studies or high-quality evidence have been produced regarding the real effectiveness of such treatment. Given the few limited kinds of research on the subject, this study aims to produce and critically evaluate other data, to establish the concrete reliability of clear aligners in orthodontic therapy. RESULTS: Significant sample sizes were obtained for intrusion, vestibulo/lingual (V/L) crown tipping, and rotation. The overall accuracy for rotation resulted in 86%, ranging from 96% for maxillary central incisors to 70.4% for mandibular first premolars. The intrusion was registered only for anterior teeth; mean predictability was 92%, with the worst result being 86.7% for mandibular canines and the best being 98% for mandibular central incisors. V/L tipping was the most accurate movement: 93.1% of the prescribed movement was completed. Maxillary central incisors showed the lowest accuracy (80.7%), while mandibular central incisors were the highest (97.5%). CONCLUSIONS: The present study provided reassuring data in support of the accuracy of the Invisalign(®) system. Vestibulo/lingual tipping was the most predictable movement, while rotation of canines, premolars, and lateral incisors were the least predictable. Intrusion resulted highly predictable up to 2 mm. When careful treatment planning follows a correct diagnosis, together with the use of auxiliary features and refinements, the planned results can be achieved in a clinically successful way. Authors believe that there is a major need for greater samples to overcome bias related to variables if we want to answer the unsolved questions, such as the predictability of severe malocclusions treatment.